Barrier islands like the Outer Banks are inherently unstable. Waves typically strike these islands at a slight angle, creating currents that pick up sand and carry it along the coast. The wave energy along the Outer Banks is unusually strong; by some estimates 700,000 cubic yards of sand, enough to fill 70,000 average-size dump trucks, moves along that stretch of coast every year.

At the new bridge, evidence of this process appeared even on opening day, in the form of long-necked black water birds called cormorants perching on a spit of sand that had formed near the north side of the bridge. That spit had not been there a few days before, said Pablo Hernandez, the transportation department engineer who managed the bridge work.